Recovery of molybdenum



Oct. 15, 1935. w R r AL 2,017,557

RECOVERY OF MOLYBDENUM Original Filed Aug. 27, 19:50

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reamed Oct. 15, 1935 UNITED STATES PATENT OFFICE 2,017,557 nEoovERY'or MOLYBDENlJM Karl Winkler and Walter Kroenlg, Ludwlgshateni on-the-Rhine, Germany, assignors to I. G. Far benindustrie Aktiengesellschaft, Frankfort-onthe-Main, Germany tcmber 27, 1929 1 Claims. (01. 23-43) The present application has been divided out from application Ser. No. 478,111, filed 27th August, 1930, Patent No. 1,923,652, August 22,. 1933, relates to the recovery of molybdenum from mix- 5 tures of molybdenum or molybdenum compounds with other metals or metal compounds.

The recovery of molybdenum from mixtures of molybdenum or molybdenum compounds with other metals or metal compounds, in particular 30 the regeneration of catalysts containing molybdenum such as are employed in the destructive hydrogenation of distillable carbonaceous materials such as coals, tars, mineral oils and the like, is of great practical importance and has hitherto 15 only been carried out with considerable losses of molybdenum.

We have now found that molybdenum may be recovered practically completely from the said mixtures, which-may contain other metals, as w for example chromium, zinc, magnesium and the like in addition to molybdenum, by subjecting the mixtures to a treatment with oxygen or gases containing or supplying oxygen such as air, nitrogen oxides or the like, at elevated temperatures 053' not exceeding 600 C. and preferably below 500 C., but usually not below 400 C. The molybdenum is usually recovered in the form of its higher oxides such as molybdic acid, according to the process of the present invention. No formation of compounds between the molybdic acid recovered and the other constituents of the mixture takes place which would injuriously afiect the subsequent further working up of the roasted .material, when carrying out the recoveryin the 35 said manner. The said temperatures are below the usual roasting temperatures of about 600 to 700 C. for the working up of ores containing molybdenum. In order to' avoid too great an increase in temperature during the oxidizing treat. ment, it is preferable to treat the material first with gases poor in oxygen, as for example the waste gases from the treatment if desiredwith the addition of inert gases such as carbon dioxide; nitrogen or the like, and toincrease the 45 oxygen content of the gases gradually so that gases rich in oxygen, as for example atmospheric air, are not used until the end of the treatment. It is advantageous to select a reaction vessel which is subdivided into several chambers so that the 50 oxidizing treatment or the material may be carried out in several fractions and stages, the conditions in each stage being more intensive than in the preceding stage.

The molybdenum oxides thus obtained are then separated from the other substances contained 5 in the resulting mixture. This separation may be carried out in different ways, as for example by treating the roasted material with ammonia and precipitating the molybdenum from the resulting ammoniacal solution at such a hydrogen l ion concentration that a complete separation oi.

the molybdic acid-from the other constituents takes place. For this purpose the roasted material may be exposed to the action of aqueous ammonia, for example of from to per cent strength, in a continuously working apparatus consisting of several extraction vessels so that the molybdenum passes into solution quantitatively in the form of ammonium molybdate. During the subsequent precipitation of the molybdenum from this ammoniacal solution, which ,is effected by acidification for example with hydrochloric acid, the maintenance of a definite hydrogen ion concentration is important because if the hydrogen ion concentration is too high part of the molybdic acid readily dissolves again, whereas if the hydrogen ion concentration is too low there is a danger that the precipitate may contain more or less large amounts of the constituents other than molybdenum in the form of molybdates. The optimum value of the hydrogen ion concentration may be readily determined by a preliminary experiment on a small scale.

Another method of working up the roasted material is by treating it with suitable acids, and. if necessary with an oxidizing agent, in order to dissolve out the constituents other than molybdenum. For this purpose dilute hydrochloric acid may be used as the acid and nitric acid as the oxidizing agent. The molybdic acid remains practically undissolved and may be readily separated from the resulting solution from which the other constituents of the initial material may be recovered in any known or suitable manner. When, according to the present invention, it is desired to regenerate catalysts containing molybdenum, especially the catalysts employed in the destructive hydrogenation of carbonaceous materials such as tars, mineral oils, coals and the like in the liquid phase and which, after use, frequently contain considerable amounts of impurities, especially of an orgnaic nature, it is preferable to subject the catalysts to a purification before roasting them. For this purpose, agents which dissolve the impurities or cause them to after having been suitably preheated in chamber i separate in, flocks, the flocks being decanted off, may be mixed with the catalysts, and the mixture centrifuged, a catalyst mass free from impurities being thus obtained which may be directly worked up as hereinbefore described.

The following examples will further illustrate the nature of this invention, but the invention is not restricted to these examples.

Example 1 One metric ton of acatalytic mass of 30 per cent of molybdic acid, 10 per cent of chromium oxide and 60 per cent of oil, which has been taken out from a high-pressure vessel used for the destructive hydrogenation of coals, tars, oils and the like in the liquid phase, is diluted at 100 C. with one metric ton of a middle oil of low ,boiling point and is centrifuged in a rapidly rotating overflow centrifuge 1 meter in diameter at a speed of 1700 revolutions per minute. The resulting catalyst pulp is again made into a paste with middle oil or heavy benzine and centrifuged again. The resulting catalytic mass is supplied to a drying chamber in which-the middle oil or heavy benzine isexpelled at a temperature of 350 C. The catalytic mass which no longer contains any oil, is brought in the form of layers about 20 millimeters thick on to plates arranged one above the other on small trucks. The roasting is carried out in a furnace consisting of for example six chambers, which furnace will now be further described with reference to the accompanying diagram, illustrating in plan view the arrangement of the said chambers and the manner of conducting the air therethrough. The furnace consists of six chambers I, 2, 3, t, 5 and 6, arranged one behind the other, of which chamber l serves for preheating the mass to the roasting temperature. The mass is introduced into the aforesaid chamber I by means of the aforesaid small trucks which are subsequently brought into the following chambers, so that the mass is passed through all of said chambers. In the chambers 2, 3, l and 5 the catalyst,

I, is subjected to a careful roasting at from 460 to 480C. -For this purpose, air preheated in a preheater I 'is introduced into chamber 5 by way of a pipe 8.v It is then passedintc chambars 4, 3 and 2 by way of pipes 9, I0 and II, re- I -spectively, and finally withdrawn from chamber 2'by way of pipe l2. Inthis way, the preheated atmospheric air is introduced into the chamber,

through which the material passes last, and the air is then led consecutively through the single chambers lying before the said last chamber. In this manner, the freshly introduced material is exposed to the gas which is poorest in oxygen in the first treating chamber, while in the subsequent chambers the content of oxygen gradually increases until the material in the last treating chamber is exposed to fresh atmospheric air. This has the advantage that the temperature can be accurately regulated so that the heat tone connected with the roasting process does not exceed the maximum permissible limit according to the description hereinbefore given. The regulation of the temperature is of great importance because even at temperatures above 500 C. the

molybdic acid formed by the roasting enters into combination with chromic acid and this renders a quantitative working up of the roasted material diflicult. The formation of this compound may be detected by a change in color of the roasted material from grey-green via pale yellowbrown to rose color. The waste gas leaving the apparatus is practically pure nitrogen which, if necessary after purifying it from carbon dioxide and sulphur dioxide, may be used for any desired purpose. If desired, a portion of it may be added to the fresh air, sucked in by the fan l3, by way of pipe M. The roasted catalyst is then conveyed into chamber 6, wherein it is cooled. It is then treated at about-80 C. with from 5 to 10 per cent aqueous ammonia in several extraction-vessels arranged one behind the other (not shown in the drawing). The fresh material is in the last vessel in which it comes into contact with ammonia water which has already been used in the preceding vessels. The extraction liquid enriched with ammonium molybdate passes from the last vessel to a vaporizer where a part of the ammonia water is evaporated and supplied to the first vessel in which is situated material which has already been extracted to a large extent. It is preferable to cause the ammonia water to flow upwards during the extraction in order to avoid the clogging of the plate or filter support ing the material to be extracted which it is not always possible to avoid when the aqueous ammonia flows downwards. At the end, chromium oxide, in some cases together with other sub= stances which have been added to the catalyst, such as kaolin, alumina and the like remains on the plate or filter while the molybdenum is dissolved quantitatively in the form of ammonium molybdate. This solution isthen worked up into solid ammonium molybdate or molybdic acid in any known orsuitable manner.

Example 2 50 kilograms of a catalytic mass containing molybdic acid and zinc oxide in molecular proportions is roasted at 480C. as described in Example 1 and then treated at C. with liters of 12 per cent hydrochloric acid in a stirring vessel. 20 liters of 25 per cent nitric acid are then Example 3 magnesium by reason of a kind of peptization. 70

The amount of hydrochloric acid is selected so that a quantitative precipitation of the molybdic acid is effected and so that the magnesium and zinc pass into solution. Care should be taken .that the liquid has such a hydrogen ion concentration that the resulting precipitate contains no zinc molybdate and on the other hand the hydrogen ion concentration should. not be so high that molybdic acid passes into solution again. which can be detected by a deepening in the shade of color. When the necessary amount of hydrochloric acid has been added, the solution is kept at 90 C. for a further 1 to 2 hours and then-cooled to 20 C. The molybdic acid is then separated by centrifuging or filtering by suction. It may be washed with 1 per cent hydrochloric acid or 3 per cent ammonium chloride solution.

What we claim is:

1. A process for the recovery of molybdic acid from a mixture comprising molybdenum and a constituent comprising another metal soluble in acids after roasting said mixture which comprises roasting the said mixture by treatment with a gas comprising oxygen at 'a temperature not exceeding 600 C. and treating the roasted mixture containing the molybdenum in the form of its oxides with an acid in an amount and con.- centration which will dissolve out from the roasted mixture only, but at least substantially, the constituent comprising said other metal, and simultaneously with an oxidizing agent.

2. A process for the recovery oi. molybdic acid from a mixture comprising molybdenum and a constituent comprising. another metal soluble in acids after roasting said mixture which comprises roasting the said mixture by treatment with a gas comprising oxygen at a. temperature not exceeding 600 C. and treating the roasted mixture containing the molybdenum in the form ofits oxides with a. mixture 01' hydrochloric acid and nitric acid, in an amount and concentration which will dissolve out from the roasted mixture only the constituent comprising said other metal.

3. A process for the recovery of molybdic acid from a mixture comprising molybdenum and a constituent comprising another metal soluble in acids after roasting said mixture which comprises roasting the said mixture by treatment with a gas comprising oxygen at a temperature between 400 Y and 600 C. and treating the roasted mixture containing the molybdenum in the form otits oxides with an acid in anamount and concentration which will dissolve out from the roasted mixture only, but at least substantially, the constituent comprising said other metal, and simultaneously with an oxidizing agent.

4. A process for the recovery of molybdic acid from a mixture comprising molybdenum and a constituent comprising another metal soluble in acids after roasting said mixture which comprises roasting the said mixture by treatment with a gas comprising oxygen at a temperature between 400 and 500 C. and treating the roasted mixture containing the molybdenum in the form of its oxides with an acid in an amount and concentration which will dissolve out from the roastture containing the molybdenum in the form ofv its oxides with a mixture of hydrochloric acid and nitric acid, in an amount and concentration which will dissolve out from the roasted mixture only the constituent comprising said other metal.

6. A process for the recovery of molybdic acid from a mixture comprising molybdenum and a,

constituent comprising another metal soluble in acids after roasting said mixture which comprises roasting the said mixture by treatmentwith a gas comprising oxygen at a temperature between 400 and 500 C. and treating the roasted mixture containing the molybdenum in the form of its oxides with a mixture of hydrochloric acid and nitric acid, in an amount and concentration which will dissolve out from the roasted mixture only the constituent comprising said other metal.

7. A process for the recovery of molybdic acid from a mixture comprising molybdenum and another metal selected from-the group consisting of chromium, zinc and magnesium which comprises roasting the said mixture by treatment with a gas comprising oxygen at a temperature not exceeding 600 C. and treating the roasted mixture containing the molybdenum in the form of its oxides with an acid in an amount and concentration which will dissolve out from the roasted mixture only, but at least substantially, the constituent comprising said other metal, and simultaneously with an oxidizing agent.

KARL WINKLER.

WALTER KROENIG. 

